The hydrological archetypes of wetlands

Abstract

Wetlands are valuable and diverse environments that contribute to a vast range of ecosystem services, such as flood control, drought resilience, and carbon sequestration. The provision of these ecosystem services depends on their hydrological functioning, which refers to how water is stored and moved within a wetland environment. Since the hydrological functions of wetlands vary widely based on location, wetland type, hydrological connectivity, vegetation, and seasonality, there is no single approach to defining these functions. Consequently, accurately identifying their hydrological functions to quantify ecosystem services remains challenging. To address this issue, we investigate the hydrological regimes of wetlands, focusing on water extent, to better understand their hydrological functions. We achieve this goal using Sentinel-1 SAR imagery and a self-supervised deep learning model (DeepAqua) to predict surface water extent for 43 Ramsar sites in Sweden between 2020 and 2023. Clustering analysis grouped the wetlands based on the water extent predictions into five archetypes based on their hydrological similarity: "spring-surging", "spring-flooded", "summer-flooded", "slow-drying", and "summer-dry". The archetypes represent great heterogeneity, with flashy regimes being more prominent at higher latitudes and smoother regimes found preferentially in central and southern Sweden. Additionally, many wetlands show exceptional similarity in the timing and duration of flooding and drying events, which only became apparent when grouped. We attempt to link hydrological functions to the archetypes, whereby headwater wetlands, such as spring-surging wetlands, have the potential to accentuate floods and droughts, while slow-drying wetlands, typical of floodplain wetlands, are more likely to provide services such as flood attenuation and water storage during low flow conditions. Additionally, although wetlands can be classified in a myriad of ways, we propose that classifying wetlands based on the hydrological regime derived from water surface extent is useful for identifying hydrological functions specific to the site and season and when discharge or water level data are not available. Lastly, we foresee that hydrological-regime-based classification can be easily applied to other wetland-rich landscapes to better understand the hydrological functions and identify their respective ecosystem services.